WO2009121865A1 - Emergency braking system of a machine tool - Google Patents

Abstract

The invention relates to an emergency braking system (10) of a machine tool, for abruptly braking a rotating shaft (16) of the machine tool, said system comprising at least one brake drum (12) and at least one brake shoe (18) which engage with each other in order to brake the shaft (16). According to the invention, the braking engagement of the brake drum (12) and the brake shoe (18) takes place under the influence of a centrifugal force resulting from the rotation of a shaft (16).

Description

 description

title

Emergency brake system of a machine tool

State of the art

The present invention relates to a protection system for a machine tool, in particular for a circular saw, which develops its protective effect within a very short period of time, which is usually in the range of a few milliseconds, in order to protect a user of the machine tool against injury in dangerous situations.

At present, there are essentially three different approaches to the realization of such a protection system for table and format circular saws, which is intended to prevent a user comes into contact with the rotating saw blade or carries a momentous cutting injury.

The protection system of an American manufacturer, which is marketed and sold under the name Saw Stop Inc., is an emergency braking system which enables braking of the machine tool as a result of direct engagement of a brake actuator with the saw blade, as soon as a correspondingly designed sensor has detected a dangerous situation , In this case, by using a hot-wire trigger, a rotatably arranged aluminum block is pushed into the toothing of the running saw blade with the aid of a prestressed spring which wedges therein and in this way absorbs the rotational energy of all the geometries of the machine tool rotating during the sawing process. As a side effect, this one-sided force attack on the cutting is used to sink the saw blade through a structurally specially designed suspension, which is arranged on the saw table in the saw table. With the help of this arrangement one is to be able to avert serious physical damage from the operator of the machine tool triggering the protective mechanism. The disadvantage here is the direct attack on the machining tool, ie on the cutting edge geometry of the saw blade, as caused by breaking parts of the teeth additional risk potential for the operator. Furthermore, to restore the readiness of the protection system, an exchange of the brake unit, including the saw blade, by a ready-to-use replacement unit is required, which the operator must stockpile in order to be able to continue working after the braking operation while using the protective function. This is associated with significant follow-up costs and time required for procurement and installation. In addition, it can be assumed that all components affected by the braking process, ie all circumferential geometries of the machine tool, are subjected to heavy loads during the deceleration phase. Neither the manufacturer nor corresponding publications on this system provide data regarding the fatigue strength of the system.

Another approach involves the use of a protection system for the sole lowering of the saw blade in the saw table, without initiating a braking action of the saw blade. With the help of a pyrotechnic Zündsatzes here the saw blade including the main shaft and their storage is removed from the danger zone, so that serious injury to the operator can be prevented. A disadvantage of this Schutzsystemart is the need for the movement of relatively large masses in the form of the arrangements to be lowered under strict timing in the millisecond range. The thus necessary pyrotechnic detonators, which prove to be indispensable for this protection actuators, also call for an expensive Teilreversibilität forth, which limit immediate further work on the machine tool with an operational protection system both in terms of time and organization. Furthermore, this protection system is suitable for reasons of limited space and very specific procedure only for larger stationary equipment, such as table-top circular saws that allow such a structure in their interior. On the other hand, this system is not suitable for use on smaller hand-held devices, such as miter saws or panel saws. A disclosure from a publicly funded project called "Cut-Stop" (VDI / VDE / IT) on a protection system for sliding table saws from the Institute for Machine Tools (IFW) of the University of Stuttgart describes an approach which by means of a special form of disc brake system, namely a self-reinforcing wedge brake , which brings the main shaft of the machine tool and thus the saw blade to a standstill. Here, a wedge is accelerated with the aid of a pyrotechnic igniter and then encountered between a fixed wedge guide in the form of a modified caliper and the rotating brake disc. For the selection and combination specific wedge angle α and brake pad values μ, the arrangement acts self-locking, so that with this structure depending on the inertia to be delayed, the respective time requirements for the braking operation can be met. The disadvantage of this protection system, however, lies in the fact that here as well, as described in the cited publication, an exchange of the complete brake unit due to the wedging in the friction pairing is required following the triggering of the protection actuator. The time required for the work to be done amounts to approximately 10-12 minutes for the complete restoration of system readiness. Thus, here too, a partial restriction of immediate system reversibility applies.

From DE 195 36 995 Al a safety brake for lifts is known, which has a device which decelerates the drive with a speed-dependent delay when exceeding a predetermined maximum speed of the means of transport And if necessary. also stops. The safety brake of DE 195 36 995 Al acts speed-dependent directly on the traction sheave of the rope-driven conveyor system and is able to limit their rotational speed. The safety brake designed as a centrifugal brake additionally has a device for increasing the braking force as a function of the conveying speed.

Starting from this prior art, it is an object of the present invention to provide a protective system for a machine tool of alternative construction, which develops its protective effect within a few milliseconds and at least partially overcomes the problems described above. Disclosure of the invention

To achieve this object, the present invention provides an emergency brake system for abrupt braking a rotating shaft of a machine tool, wherein the emergency brake system comprises a brake drum and at least one brake shoe, which are brought together for braking the shaft. According to the invention, the brake drum and the at least one brake shoe are designed and arranged such that the brake engagement between the brake drum and the brake shoe takes place under the influence of the centrifugal force or centrifugal force resulting from the rotation of the shaft.

The present invention is therefore geared to the delay of the rotating shaft of the machine tool, which may be, for example, a table saw, a miter saw or a panel saw, by using the existing rotational energy of the rotating shaft by means of Construction of a self-reinforcing or self-locking friction pair to realize.

It should be clear that the triggering of the deceleration process, which takes place, for example, in response to an output signal of a sensor that detects a hazardous situation for the user, mechanically, electromechanically, pyrotechnic, pneumatic or hydraulic can be done and is in principle not bound to any particular medium, however, electromechanical triggering is preferred due to a simple construction and very good reversibility.

Advantageously, when the machine tool is being decelerated, it does not intervene directly in the tool. Such an intervention would inevitably go hand in hand with the destruction of the tool. The machine tool according to the invention brakes the shaft driving the tool directly or indirectly. In this way, the tool itself remains undamaged.

The desired short braking time by means of the centrifugal acceleration of at least one brake partner can be optimized by the exact tuning of the friction required for the braking. Advantageously, at least one or even both brake partners, ie brake drum and / or brake shoe (s) have a friction - -

covering, which increases the friction and thereby increases the braking effect and reduces the braking time. The friction pairing and their functionality depend decisively on the choice of materials of the friction partners.

It should be noted that in the present case emergency braking is involved which does not fall within the scope of normal machine operation and therefore occurs very rarely. At the time of the occurrence of an emergency, however, a possible violent deceleration of the shaft and thus the tool should be initiated, which also eliminates any claims to a possible metering of the braking effect or, for example, low wear behavior of the friction pair, as is typically the case in other applications ,

Thus it can be foreseen that due to this desired deceleration characteristic and the consequent choice of materials, friction pairings result which deviate from those used in ordinary friction brakes, for example those used in the vehicle sector, since there are other requirements for braking behavior. In this way, the predetermined time frame of the deceleration, which is in the range of a few milliseconds, can be guaranteed. The inventive design of the brake allows the deceleration of a directly or indirectly driven by a shaft tool in very short times, which are typically in the range of 1 to 50 ms, advantageously in the range of 1 to 20 ms and in particular in the range of 10ms and less.

The material selection of the friction partners is to be made so that the resulting friction pair is in close coordination with the geometry of the entire system. In the special case of the present braking device of a machine tool, this means that the achievable friction coefficients μ must be as large as possible in order to achieve the best possible delays in the range of a few milliseconds for a given geometry of the main components.

This is achieved in an advantageous manner in that at least one lining zone is formed on the brake pad, which has self-locking properties.

Due to the initiated in this way braking consequently results in large loads on the pads and brake drum, so that for the sake of a limited - -

Installation space in the present case, the drum is advantageously made of steel or a similar resilient material. In order nevertheless to have an influence on the material of both friction partners, at least one of the brake partners, but advantageously both are provided with a friction lining. So it may be useful from a technical point of view, for example, to install a friction insert, for example in the form of a friction ring of materials described below in more detail within the brake drum.

This friction ring can be pressed and / or clamped or similarly fastened, for example, to allow a firm connection to the brake drum and thus support the loads occurring. In order to absorb the forces occurring in the event of a brake, it is also possible to use a Nu1 / spring connection between the brake drum and the friction ring.

The brake shoes of the system, which are typically also formed of steel advantageously have a friction lining. The friction lining, for example, a sintered material, in particular of the material MD517, can be glued to the brake shoes, screwed on, or else securely fixed by other attachment methods, such as tongue and groove. In order to be able to absorb the forces occurring in the braking event on the brake shoe side as well, the brake lining can be secured against displacement against the direction of movement of the brake shoe via a support on the brake shoe.

It makes sense for the friction or brake partners to have friction surfaces made of different materials. Subsequent materials and all resulting material pairings of the friction partners are for the o. G. Use considered promising:

Sintered coating (egMD517) aluminum soft (eg AI 24b249) aluminum hard (eg AI Ia2) polyamide PA6.6 glass fiber reinforced polyamide PA12 polyamide POM polyurethane Organic friction lining

copper

Brass

It is advantageous that the friction lining of the brake drum side friction partner has a harder material than the brake shoe side friction partner. For example, the use of MD517 sintered linings on aluminum is a suitable combination. In this case, the friction ring of the brake drum could consist of aluminum and one or more brake shoes could have a sintered lining of MD517.

The reverse arrangement is also conceivable.

According to one embodiment of the present invention, the at least one brake shoe is pivotally mounted on a brake shoe carrier, which is arranged on the rotating shaft and rotates with it. Preferably, a locking device is provided which is adjustable between a locked position in which the brake shoe is held on the brake shoe carrier, and an unlocked position in which the at least one brake shoe is released such that it performs a pivoting movement in the direction of the brake drum to generate the braking intervention. In other words, the rotating with the rotating shaft at least one brake shoe is abruptly moved within a few milliseconds in the direction of the stationary brake drum by utilizing the centrifugal force of the rotating shaft, as soon as the locking device is transferred to its unlocked position.

The locking device preferably comprises at least one locking element, which is movable between a locked position, in which it is in engagement with the at least one brake shoe, and an unlocked position, in which it is decoupled from the brake shoe. Such a blocking element may be formed, for example, as a locking pin or the like.

The locking device advantageously comprises an actuator which transfers the locking device from the locked position to the unlocked position. This actuator may, for example, be a magnetic actuator which pulls a ring anchor to which a blocking element in the form of a blocking element is attached. is bolted to disengage the locking pin from the brake shoe, so that it is released.

The emergency brake system also preferably includes a coupling device adapted to connect the braked shaft to a driveline in its coupled position, and to be automatically transferred to its decoupled position during emergency braking in which the drive shaft to be braked decouples from the driveline is. Such decoupling of the drivetrain during an emergency braking operation ensures that the driveline, which may have, for example, a drive shaft and possible gear ratios, is excluded from the actual braking operation, whereby the drivetrain is not exposed to the large deceleration torques occurring during the braking process. This brings on the one hand the advantage that components of the drive train can not be damaged due to the braking process. On the other hand, the geometries of the drive-side components do not have to be structurally adapted to the requirements of the braking process, which is why they can be produced less robust and less expensive. In addition, this results in a beneficial reduction of the moment of inertia to be delayed, since the components of the drive train do not have to be braked. Thus, the system load during the deceleration phase can be significantly reduced. Accordingly, the time required for the deceleration of the saw blade can be significantly reduced with the same force. Alternatively, of course, the force can be reduced with unchanged Abbremszeitdauer.

According to a preferred embodiment, the shaft to be braked is designed as a hollow shaft, in the cavity of which a drive shaft of the drive train is positioned. The coupling device is advantageously formed by a provided on the at least one brake shoe projection which engages in the coupled position provided by a shaft to be braked through hole in a recess of the drive shaft, so that the drive shaft and the shaft to be braked rotatably connected to each other, and which comes in the decoupled position out of engagement with the recess of the drive shaft, so that the braked shaft is no longer driven by the drive shaft. In this way, a decoupling of the drive train during Abbremsvor- be realized. Preferably, the projection engages with the recess in a form-fitting manner, whereby a secure engagement of the projection in the recess is achieved. For this purpose, the projection, for example, arcuate and the recess may be formed prismatic.

It should be noted that the number of projections does not have to correspond to the number of recesses. For example, four recesses and only two projections may be provided. This is advantageous in that the drive shaft only has to be rotated slightly after a triggering of the emergency brake system in order to re-arrange the projections in a pair of recesses. Also, more than two brake shoes can be provided, of which, however, only two must be established via corresponding formed from a projection and a recess connections to the drive shaft.

In addition, the emergency brake system according to the invention preferably has a restoring device for moving the at least one brake shoe back into its starting position in order to ensure complete system reversibility after the deceleration process has taken place. The restoring device is designed in close coordination with the self-reinforcement of the friction pair and thus with the geometry of the brake system. The restoring device can be realized, for example, both by the use of appropriately sized tension and compression spring elements.

In addition, the present invention relates to a machine tool with an emergency brake system of the type described above, wherein the machine tool is preferably a circular saw, more specifically a table saw, a miter saw or a panel saw.

However, it should be clear that the braking system according to the invention can also be applied to other machine tools which, for specific reasons, depend on a specifically triggerable delay within a given time frame in the range of a few milliseconds. An adaptation of this invention to another machine tool is therefore possible in a particular case in principle. embodiment

Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. In it is:

Fig. 1 is a schematic front view of an emergency brake system according to an embodiment of the present invention in a state in which the braking operation has not been triggered;

FIG. 2 is a schematic front view of the emergency brake system shown in FIG. 1 in a state in which the deceleration operation has been initiated; FIG.

Fig. 3 is a longitudinal sectional view of the emergency brake system shown in Figs. 1 and 2 in a condition in which the braking operation has not been initiated;

4 is a schematic longitudinal sectional view of the emergency brake system shown in FIGS. 1 to 3 in a state in which the braking operation has been initiated;

Fig. 5 is a schematic cross-sectional view of the emergency brake system shown in Figs. 1 to 4 in a state in which the braking operation has not been triggered;

Fig. 6 is a schematic cross-sectional view of the emergency brake system shown in Figs. 1 to 5 in a state in which the braking operation has been initiated;

Fig. 7 shows a brake shoe of the emergency brake system according to the invention with friction lining

8 shows a schematic cross-sectional view of an embodiment of the emergency braking system according to the invention for a circular saw; 9 is a table saw with a braking device according to the invention as a possible embodiment of a machine tool according to the invention in a side view.

Fig. 10, the table saw of Figure 8 in a plan view.

Figures 1 to 6 are schematic views of an emergency brake system according to an embodiment of the present invention, generally designated by the numeral 10, serving, for example, a saw blade of a table saw (not shown here, but rather Figures 9 and 10) in a hazardous situation within a very short period, which is in the range of a few milliseconds, to a standstill. The emergency brake system 10 includes a fixed brake drum 12 which is secured to a frame member of the table saw, not shown. This frame component must be constructively designed so that it can withstand the braking torque generated during the deceleration phase and can absorb it. Further, the emergency brake system 10 includes a brake shoe carrier 14 which is fixedly connected to a saw blade side output shaft 16 so that it rotates with this in the direction indicated by the arrow 17 rotation. On the brake shoe support 14 two diametrically opposed brake shoes 18 are fixed, which are each rotatably mounted about a pivot pin 20. The brake shoes 18 are provided on their facing the brake drum 12 each surface with a friction lining 22, said friction linings 22 come during a braking operation of the emergency brake system 10 with the fixed brake drum 12 into engagement, so that the friction linings 22 and the brake drum 12 form a friction pair. The brake drum 18 may itself also have a friction lining 22, but the material of which does not have to be identical to the material of the friction linings 22 of the brake drum 12.

In the state shown in Fig. 1, in which the braking operation has not been triggered, the brake shoes 18 are held by means of locking pin 24 fixed to the brake shoe carrier 14 so that they can not rotate about the pivot pin 20.

These locking pins 24 are part of a locking device 26, which also has a magnetic actuator 28, with which the locking pin 24 between a locking th position in which the brake shoes 18 are held on the brake shoe carrier 14, and an unlocked position are adjustable in which the brake shoes 18 are released such that they perform a pivoting movement about their pivot pin 20 in the direction of the brake drum 12 to the braking engagement between the friction linings 22 and the brake drum 12 to produce. As shown in FIG. 3, the solenoid actuator 28 of the latch 26 is fixedly secured to the output shaft 16. Alternatively, the magnetic actuator 28 may also be attached to a non-stationary, stationary housing part and act contactlessly on the locking pin 24. The locking pins 24, which are movable back and forth by the solenoid actuator 28, extend through provided in the brake shoe 14 through holes 30 and engage in the state shown in FIGS. 1, 3 and 5, in which the braking process has not yet initiated was, in engagement openings 32, which are provided in the brake shoes 18, respectively. In this way, the brake shoes 18 are locked to the brake shoe carrier 14. In the case of triggering the brake system, the solenoid actuator 28 pulls a ring anchor to which the locking pin 24 are attached to a defined release travel s from the brake shoe 14 and thus releases the brake shoes 18, see Fig. 4. These lie down as a result of centrifugal forces generated by the rotating output shaft 16 and the centrifugal acceleration to the fixed brake drum 12, whereby the required for delaying the output shaft 16 friction pair between the friction linings 22 of the brake shoes 18 and the brake drum 12 is formed. Although the locking pin 24 in the present embodiment with the aid of the magnetic actuator 28 moves back and forth, it should be noted that the locking pin 24 can be moved alternatively also under the action of a spring force or the like in one of the two directions of movement. Thus, the forward movement of the locking pin 24 can take place under the influence of the magnetic actuator 28, while the deferral of the locking pin 24 is effected by one or more spring elements, or vice versa.

Depending on the geometric dimensions of the construction, its amplification factor C ^{* is} defined, which, for the present design, must be within the range of self-reinforcement or self-locking of the system. For this case, only a short impulse to form the friction pairing is required because the brake shoes 18 are pressed due to the force balance occurring to the brake drum 12. Due to the critical timing of the brake system mentioned, it seems to be expedient, inter alia, to choose a concept that allows the application of the technical principle of self-help. This means that the introduced for triggering clamping force F _{Sp is} amplified within the system by a multiple, the generated reaction force F _Reak t, here in the form of a frictional ^¬ force F _R in turn to increase the introduced clamping force F _Sp contributes. This feature is also called self-reinforcement or servo-effect. The systems characterized in this way provide in principle the lowest possible delay times using low clamping forces, so that both the mass of the tripping members and the required tripping time t _A can be minimized.

The gain factor C ^* continues to be defined as follows:

_* F ₁ . μ \ ΛK ιi

If the factor C * is positive, the forces act in the sense of direction assumed in the sketch. The frictional force F _R results here from the increased by the factor C * clamping force F _S p. For μ = tanα, the equation for C * has a pole, so that this gain tends to infinity. In this point, there is practically the system state of an unstable equilibrium. The choice of the parameters tan α <μ results in a negative amplification factor C *. This means a theoretical reversal of the sense of direction of the clamping force F _s p, which would have to occur in order to maintain the equilibrium of forces. In reality, this case denotes a special state of a self-reinforcing system. The friction pad is additionally pressed by the resulting friction force F to the treadmill. Due to the resulting, continuous, mutual increase in the friction and normal forces occurs in the ideal case after a short time stiction within the friction pairing. This leads in consequence to the blocking of the entire system. In this context is commonly spoken of self-locking. In this case, forces occur which are greater than the forces mediated by the centrifugal force of the brake shoes. As a function of the relative coefficient of friction μ of the friction partners, angles α thus result, denoting areas in which self-reinforcement or self-locking occurs.

As can be seen in particular from FIGS. 3 and 4, the output shaft 16 to be braked with the aid of the emergency brake system 10 is designed as a hollow shaft, in the cavity of which a drive shaft 34 is accommodated, which forms part of the drive train (not shown). In order to connect the output shaft 16 and the drive shaft 34 rotatably with each other, on the brake shoes 18 in the direction of the center of the output shaft 16 and the drive shaft 34 protruding arcuate projections 36 are formed, each through through holes 38 which are provided in the output shaft 16 through engage and engage in prismatic recesses 40 of the drive shaft 34, as shown in Fig. 5. By the engagement of the provided on the brake shoes 18 projections 36 in the corresponding recesses 40 of the drive shaft 34, the output shaft 16 and the drive shaft 34 rotatably connected to each other. If the braking operation is initiated starting from the state shown in FIG. 5, the brake shoes 18, after the locking pins 24 have been pulled out of the brake shoes 18 by the release travel s, rotate about their respective pivot pins 20 in the direction of the brake drum 12, so that the on the brake shoes 18 arranged projections 36 come out of engagement with the associated recesses 40 of the drive shaft 34, whereby the drive shaft 34 is decoupled from the output shaft 16. This decoupling does not expose the powertrain to the decelerating moments generated during the deceleration process so that it can not be damaged. In addition, it is possible to make the components of the drive train less robust, since they are not subject to high loads during the deceleration process. Thus, for example, the cross section of the motor-side drive shaft 34 can be made smaller than in the case in which no decoupling device is provided for decoupling the drive train. However, the decisive advantage is that the number of components to be delayed is reduced to a minimum. This has a positive effect on the system load during the deceleration phase, as previously described. - -

Due to the above-described structure of the emergency brake system 10, the brake release time interval can be greatly shortened because the brake engagement between the brake drum 12 and the brake shoes 18 is under the influence of the centrifugal force resulting from the rotation of the output shaft 16.

In addition, the construction shown in FIGS. 1 to 6 realizes an electromechanical system without the use of other forms of energy, which under certain circumstances endanger the complete reversibility and would be a limitation for this.

Due to the use of a two-sided attack of Reibumfangskraft the friction pairing, the present rolling bearings are spared and must not be revised or even redesigned due to concerns about the durability of the overall system, which in turn increased mass inertia would be introduced into the system.

By a construction, as described herein, also circumferential outer geometries of the brake unit are avoided, whereby an easy to encapsulating, closed system can be realized with a compact design, which also integrates positively into the special concerns of occupational safety in dealing with machine tools.

It should be understood that actuation of the solenoid actuator 28 is accomplished by outputs from respective sensors that sense a condition in which an operator is dangerously close to the saw blade of the table saw. Such sensors are known in the art, which is why they have not been discussed in detail in the present description. Such sensors are known in the art, which is why they have not been discussed in detail in the present description. Radar sensors, in particular UWB radar sensors (UWB = Ultra Wide Band) and also optical sensors, in particular NIR systems (NIR = Near Infra Red) may be mentioned here by way of example and not exhaustively.

FIG. 7 shows by way of example the brake pad 18 of an emergency brake system 10 according to the invention with a friction lining 22. The brake shoes 18 of the system 10, which are typically - -

The friction lining 22, for example, a sintered material, in particular of the material MD517 if the brake lining of the drum 12 should be aluminum, can on the brake shoes 18 glued on, screwed on, or else securely fixed by other attachment methods, such as tongue and groove. In order to be able to absorb the forces occurring in the brake case on the brake shoe side, the brake pad can be secured by a support 23 on the brake shoe 18 against displacement against the direction of movement of the brake shoe.

FIG. 8 shows the emergency braking system 10 according to the invention of a circular saw in a schematic sectional drawing. The saw blade 66, is stretched over a tensioning device 68 on an output shaft 16 of an electric motor, not shown, and is driven by this shaft. With the shaft 16 to run the brake shoes 18 which are secured in the locked state of the system and not by the centrifugal force or centrifugal acceleration to the outside, i. in the direction of the housing fixed brake drum 12 are driven. The brake drum 12 is provided on the inside with a pressed-in friction ring 70, for example made of aluminum. In the application, which is detected by a corresponding sensor, the securing bolts of the brake shoes 18 are released, so that the brake shoes 18 are now driven due to the centrifugal force against the inside of the brake drum. The brake shoes 18 then interact with the friction ring 70 of the brake drum 12. To increase the friction and thus the braking effect and shorten the braking time, the brake shoes 18 on a friction lining 72, which may for example consist of a sintered material of the material MD517.

Figures 9 and 10 show an embodiment of a machine tool according to the invention, with an emergency braking system 10 and a sensor system 52 for detecting the presence of a type of material, in particular of tissue, such as the human tissue of a hand. 9 is a table saw (benchtop system) and has a recognition device 52, which is provided for detecting the presence of a type of material 54, in particular, for example, tissue in a machine tool working area 56. The device 52 for detection has at least one sensor 50, which may be installed in a plane above the working range of the machine tool, as indicated in Figure 9. Alternatively, the sensor 50 of the device 52 may also be integrated directly in the work table 40. Both possibilities can be realized both individually and simultaneously, as shown by way of example in FIG. The device 52 for detecting in particular human tissue but also other materials may include, but is not limited to, radar sensors, in particular UWB radar sensors (UWB = Ultra Wide Band) and / or also optical sensors, in particular NIR systems (NIR = Near Infra Red). include.

Upon detection, for example, of a hand 54 in the danger area immediately in front of the saw blade of the machine tool, an activity signal is generated which releases the securing bolts of the brake shoes so that they - as described in detail above - driven by the centrifugal force the brake drum 12 are driven and initiate the braking process ,

Figure 10 shows the embodiment of the table saw 48 in a side view. A motor 60 drives via a gear 63 to a tool, which is a saw blade 66 in the embodiment of FIG. The saw blade 66 is attached via a tensioning device 68 on an output shaft 16. The emergency brake system 10 is advantageously arranged between the transmission 63 and the shaft 16, i. makes it possible, in the case of activation, to decouple the shaft 16 from the driving gear 63. In the case of emergency braking overloading of the gear stage is thereby avoided. Gear stage and motor shaft are then decoupled from each other logically.

Although in the embodiment described above a circular saw was chosen as an example of a machine tool, it should be understood that the principle of the present invention is also applicable to other machine tools.

Finally, it should be clear that the previously described embodiment of the emergency braking system according to the invention is in no way limiting. Rather, modifications and changes are possible without departing from the scope of the present invention, which is defined by the appended claims.

Claims

claims An emergency braking system (10) of a machine tool for abruptly braking a rotating shaft (16) of the machine tool, comprising at least one brake drum (12) and at least one brake shoe (18) which are engaged with each other for braking the shaft (16). characterized in that the braking engagement between the brake drum (12) and the brake shoe (18) takes place under the influence of a centrifugal force resulting from the rotation of a shaft (16). 2. Emergency brake system (10) according to claim 1, characterized in that at least one of the brake partners has a friction lining (22). 3. emergency braking system (10) according to claim 2, characterized in that the friction lining (22) at least one lining zone is formed, which has self-locking properties. 4. emergency brake system (10) according to claim 2 or 3, characterized in that the friction lining of the brake drum side friction partner has a harder material than the brake shoe side friction partners. 5. Emergency braking system (10) according to claim 2, 3 or 4, characterized in that the friction lining (22) is selected at least one brake partner from a group of materials, the sintered lining, soft aluminum, hard aluminum, polyamide, in particular polyamide PA6.6 glass fiber reinforced, polyamide PA12, polyamide POM, polyurethane, copper, brass, organic material. 6. Emergency brake system (10) according to any one of the preceding claims, characterized in that the brake drum (12) has a friction ring (70) whose material is different from the material of the drum (12). 7. Emergency braking system (10) according to claim 6, characterized in that the friction ring (70) of the brake drum (12) consists of an aluminum material. 8. Emergency brake system (10) according to any one of the preceding claims, in particular according to claim 6, characterized in that the friction lining (22) at least one of the brake shoes (18) consists of a sintered material, in particular a sintered material of the material MD517. 9. emergency brake system (10) according to any one of the preceding claims, characterized in that means (23) for securing the friction lining (22) on the Reibbelagträger (12, 18) are present. 10. Emergency brake system (10) according to any one of the preceding claims, in particular, according to claim 1, characterized in that the at least one brake shoe (18) is pivotally mounted on a brake shoe carrier (14) which is arranged on the shaft (16) and with this is revolving. 11. Emergency brake system (10) according to claim 9, characterized in that a locking device (26) is provided which is adjustable between a locked position in which the brake shoe (18) is held on the brake shoe carrier (14) and an unlocked position, in which the at least one brake shoe (18) is released such that it performs a pivoting movement in the direction of the brake drum (12) in order to generate the braking engagement. 12. Machine tool with an emergency braking system (10) according to at least one of the preceding claims. 13. Machine tool according to claim 11, characterized in that the machine tool is a saw, preferably a circular saw and in particular a table saw (48).